Real-time difference imaging analysis of MOA Galactic bulge observations during 2000

We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg² were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.     

Crystallization of authigenic carbonates in mud volcanoes at Lake Baikal

This paper presents data on authigenic siderite first found in surface sediments from mud volcanoes in the Central (K-2) and Southern (Malen’kii) basins of Lake Baikal. Ca is the predominant cation, which substitutes Fe in the crystalline lattice of siderite. The enrichment of the carbonates in the ¹³C isotope (from +3.3 to +6.8‰ for the Malen’kii volcano and from +17.7 to +21.9‰ for K-2) results from the crystallization of the carbonates during methane generation via the bacterial destruction of organic matter (acetate). The overall depletion of the carbonates in ¹⁸O is mainly inherited from the isotopic composition of Baikal water.     

Cloning of cytochrome P450 1A (CYP1A) genes from the hermaphrodite fish Rivulus marmoratus and the Japanese medaka Oryzias latipes

To use two small fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae) and the Japanese medaka Oryzias latipes (Belloniformes) as testing models in molecular ecotoxicology, we have cloned the cytochrome P450 1A (CYP1A) gene after screening of both genomic DNA libraries, and sequenced 11,863 and 7,243 bp including all the exons and introns with promoter regions, respectively. The Rivulus and the medaka CYP1A gene consisted of seven exons (including non-coding exons) with high homology to mammals. In the promoter region, Rivulus CYP1A gene has seven xenobiotic response elements (XREs) and two metal response elements (MREs), while the Japanese medaka CYP1A gene has six XREs and four MREs. Interestingly, medaka CYP1A gene has a number of MREs at the promoter, which may affect its response on metal exposure. We describe here the gene structure of both fish CYP1A genes.     

Petrological feature of spinel lherzolite xenolith from Oki-Dogo Island: An implication for variety of the upper mantle peridotite beneath southwestern Japan

Abstract   Spinel lherzolite is a minor component of the deep-seated xenolith suite in the Oki-Dogo alkaline basalts, whereas other types of ultramafic (e.g. pyroxenite and dunite) and mafic (e.g. granulite and gabbro) xenoliths are abundant. All spinel lherzolite xenoliths have spinel with a low Cr number (Cr#; < 0.26). They are anhydrous and are free of modal metasomatism. Their mineral assemblages and microtextures, combined with the high NiO content in olivine, suggest that they are of residual origin. But the Mg numbers of silicate minerals are lower (e.g. down to Fo₈₆) in some spinel lherzolites than in typical upper mantle residual peridotites. The clinopyroxene in the spinel lherzolite shows U-shaped chondrite-normalized rare-earth element (REE) patterns. The abundance of Fe-rich ultramafic and mafic cumulate xenoliths in Oki-Dogo alkali basalts suggests that the later formation of those Fe-rich cumulates from alkaline magma was the cause of Fe- and light REE (LREE)-enrichment in residual peridotite. The similar REE patterns are observed in spinel peridotite xenoliths from Kurose and also in those from the South-west Japan arc, which are non-metasomatized in terms of major-element chemistry (e.g. Fo > 89), and are rarely associated with Fe-rich cumulus mafic and ultramafic xenoliths. This indicates that the LREE-enrichment in mantle rocks has been more prominent and prevalent than Fe and other major-element enrichment during the metasomatism.     

Implications of Analcime Hydrothermally Formed from Na-alumino-borosilicate Glasses Containing Cs and Sr for the Stability of High-level Radioactive Waste Form

Abstract. In order to know the behaviors of radioactive elements such as cesium and strontium during a hydrothermal alteration of borosilicate glass of radioactive waste, some alumino-borosilicate glasses belonging to the systems Na₂O-Al₂O₃-B₂O₃-SiO₂-SrO, Na₂O-Al₂O₃-B₂O₃-SiO₂-Cs₂O and Na₂O-Al₂-O₃-B₂O₃-SiO₂-SrO-Cs₂O have been treated hydrothermally at 200C under a vapor pressure of 1.54 MPa. The result shows that all glasses are changed into crystalline phases with running time up to 60 days, and that analcime-type zeolite is formed as a major product. The formed zeolite is shown to contain cesium and/or strontium. Considering the fact that natural zeolite occurs in wide physicochemical conditions including hydrothermal one, the analcime-type zeolite is expected to fix stably the radioactive elements in the disposal site. Since aluminum is necessary for the formation of the analcime-type zeolite, the waste glass should have aluminum as one of major components.     

Distribution and expression of gas seeps in a gas hydrate province of the northeastern Sakhalin continental slope, Sea of Okhotsk

Multidisciplinary surveys were conducted to investigate gas seepage and gas hydrate accumulation on the northeastern Sakhalin continental slope (NESS), Sea of Okhotsk, during joint Korean–Russian–Japanese expeditions conducted from 2003 to 2007 (CHAOS and SSGH projects). One hundred sixty-one gas seeps were detected in a 2000 km² area of the NESS (between 53°45′N and 54°45′N). Active gas seeps in a gas hydrate province on the NESS were evident from features in the water column, on the seafloor, and in the subsurface: well-defined hydroacoustic anomalies (gas flares), side-scan sonar structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking), high methane concentrations in seawater, and gas hydrates in sediment near the seafloor. These expressions were generally spatially related; a gas flare would be associated with a seepage structure (mound), below which a gas chimney was present. The spatial distribution of gas seeps on the NESS is controlled by four types of geological structures: faults, the shelf break, seafloor canyons, and submarine slides. Gas chimneys that produced enhanced reflection on high-resolution seismic profiles are interpreted as active pathways for upward gas migration to the seafloor. The chimneys and gas flares are good indicators of active seepage.     

Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal

We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ¹³C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ¹³C signatures at two sites where ethane δ¹³C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which ¹³C and deuterium were both highly depleted (mean δ¹³C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C₂ δ¹³C–δD classification for hydrate-bound gas in either freshwater or marine environments.